Android API 21 async GET请求不工作

<uses-permission android:name="android.permission.INTERNET" />

ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
    // 网络连接正常
} else {
    // 网络连接异常
}

private class MyAsyncTask extends AsyncTask<Void, Void, String> {
    @Override
    protected String doInBackground(Void... params) {
        try {
            URL url = new URL("http://example.com/api");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.connect();

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                InputStream inputStream = connection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                StringBuilder stringBuilder = new StringBuilder();
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    stringBuilder.append(line);
                }
                bufferedReader.close();
                inputStream.close();
                return stringBuilder.toString();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        if (result != null) {
            // 处理请求结果
        } else {
            // 请求失败
        }
    }
}

// 执行异步任务
new MyAsyncTask().execute();

private class MyAsyncTask extends AsyncTask<Void, Void, String> {
    @Override
    protected String doInBackground(Void... params) {
        try {
            URL url = new URL("https://example.com/api");
            HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
            connection.setSSLSocketFactory(getSSLSocketFactory());
            connection.setHostnameVerifier(getHostnameVerifier());
            connection.setRequestMethod("GET");
            connection.connect();

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpsURLConnection.HTTP_OK) {
                InputStream inputStream = connection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                StringBuilder stringBuilder = new StringBuilder();
                String line;
                while ((line = bufferedReader.readLine()) != null) {
                    stringBuilder.append(line);
                }
                bufferedReader.close();
                inputStream.close();
                return stringBuilder.toString();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        if (result != null) {
            // 处理请求结果
        } else {
            // 请求失败
        }
    }

    private SSLSocketFactory getSSLSocketFactory() {
        try {
            TrustManager[] trustAllCerts = new TrustManager[]{new X509TrustManager() {
                @Override
                public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                }

                @Override
                public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                }

                @Override
                public X509Certificate[] getAcceptedIssuers() {
                    return new X509Certificate[0];
                }
            }};
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, trustAllCerts, new SecureRandom());
            return sslContext.getSocketFactory();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    private HostnameVerifier getHostnameVerifier() {
        return new HostnameVerifier() {
            @Override
            public boolean verify(String hostname, SSLSession session) {
                return true;
            }
        };
    }
}

// 执行异步任务
new MyAsyncTask().execute();